A large part of the world's oil supplies are carried to and from the various ports and terminals by tankers and similar vessels. The latter are built in all sizes depending on the use to which they are put and the waters through which they will operate. It has, however, become economically desirable to make the tankers sufficiently large to carry increasingly larger cargos. The latter are referred to as very large cargo carriers.
As a matter of practicality all tanker hulls are segregated into a plurality of individual tanks. These tanks are connected to manifold systems which facilitate the simultaneous carrying of different liquids to and from various ports. Thus, a ship's cargo can embody at any one time a number of different liquids, whether they be in refined or crude form.
In the instance of crude oil carrying vessels, the crude liquid, as it is brought from the ground, normally carries with it considerable amounts of solids and foreign materials. This is understandable since the normal reservoir for the crude which is forced from the ground, is generally formed of either rock or clay or similar forms of substrate.
In any event even though the crude as it is received from the ground is quite flowable, it nonetheless carries with it a substantial portion of solid material. This latter will, when the crude is permitted to stand for any period of time, tend to separate or settle out from the liquid. Thus, as the solid components are normally heavier than the liquid, the solid faction will gravitate to the bottom of the storage tank and gradually accumulate to a depth of from several inches to several feet.
Further, the deposits on the tank floor will include muddy waters, rusty water, and mud.
This semisolid or highly viscous liquid mass is generally referred to as sludge. Its presence on the vessel is undesirable for several reasons. First, when the vessel's tanks are holding sludge it is undesirable to carry any refined liquid or petroleum since a certain amount of the sludge will be picked up and carried along with the refined product. Further, when the sludge is permitted to lie for a period in a closed or even a semiclosed tank it will tend to gasify and promote an explosive atmosphere within the tanks.
It is therefore standard procedure when transporting crude products over water between two points, that periodically the vessel's tanks be cleaned out. This cleaning normally removes the sludge and other solid accumulations from the floor of the tank. The cleaning further embodies a degassing process which removes any gaseous product which may have accumulated in the tank.
There are a number of known and practical ways of removing sludge such that it can either be processed, or deposited in a separate holding tank or vessel. It can thereafter be disposed of either economically, or in any manner desired to avoid pollution of the environment.
At present, tankers are equipped with various means and systems for dealing with sludge. However the most common expedient resorted to for cleaning the vessel's tanks, is by the removal of the sludge manually, using the simplest of implements. The process in any event is both time consuming and expensive.
In some instances sludge can be removed from the tanks while the vessel is in transit. Thus all the solids are deposited in a separate holding tank. Such an operation can also be achieved while the vessel is at anchor, while moored to a tug, or while in dry dock. In any event the sludge is removed by an operation that mandates considerable expense as well as loss in operating days.
In the presently disclosed invention means is provided within a tanker for transferring cargo to and from the various holding and liquid storage tanks. Toward achieving a relatively inexpensive cleaning operation, the tanker is provided with means for connecting into either the main, or into a stripper offloading system. Thus, a portable discharge unit is removably connected to any of the individual cargo ingesting connections which are located within the respective tanks. By actuating the discharge or eductor system, sludge can be readily removed from the tank and collected, or otherwise disposed of.
It is therefore an object of the invention to provide a tanker cargo discharge or offloading system that is capable of achieving an economical and quick cleaning of the vessel's tanks.
A further object is to provide a cargo discharge system for a tanker which is capable of reaching into all parts of the vessel's storage tanks to reach accumulations of sludge which ordinarily remain at the tank's floor as a viscous residue.
Still another object is to provide a portable sludge offloading apparatus capable of removably connecting to a vessel's cargo offloading system whereby activation of the latter will cause the sludge to be ingested and removed from the vessel's respective holding tanks.